The present invention relates, in general, to forming optical images and, more particularly, to forming multiple images of an object.
Typically, work pieces such as semiconductor devices are visually inspected to insure that they meet design specifications for parameters such as lead coplanarity, lead length, lead straightness, mark inspection, surface inspection, lead pitch, etc. A semiconductor device under inspection is usually placed on a visual inspection station. Using either front lighting or back lighting technique, images of the device are formed and analyzed using a vision computer.
Certain types of inspections require multiple views of the device. This can be achieved using multiple illuminations. Different illuminations providing different views sometimes interfere with each other. For example, the illuminations for dark field image and bright field image interfere with each other. Multiple back lighting illuminations used for generating multiple shadow images of the device also interfere with each other. Illuminating the device with one light beam at a time and forming multiple images of the device sequentially will avoid the interference. This requires the device to be stationary over the whole time interval of changing illuminations and acquiring multiple images. An inspection process using such techniques is complicated and time consuming.
Accordingly, it would be advantageous to have an apparatus and a method for acquiring multiple images of an object. It is desirable for the apparatus to be simple and inexpensive. It is also desirable for the method to be time efficient. It would be of further advantage for the apparatus and the method to be compatible with existing equipment and inspection process.